Jon Udell at InfoWorld - Accessing the web of databases:
"I’ve always regarded the Web as a programmable data source as well as a platform for the document/software hybrid that we call a Web page. Early on, programmable access to Web data entailed a lot of screen scraping. Nowadays it often still does, but it’s becoming common to find APIs that serve up the Web’s data.
[...] Free text search is an even more popular access API. Nearly every site provides that service, or outsources it to Google or another engine.
[...] What you can’t typically do, though, is create mashups by running ad hoc queries against remote Web data. There are good reasons to think that it’s just crazy to export open-ended query interfaces over the Web. No responsible enterprise DBA would permit such access to the crown jewels. But there are all kinds of data sources -- or what Idehen likes to call data spaces -- and a range of feasible and appropriate access modes."